1. Field of the Invention
The present invention relates to a method of evaluating the characteristics of superconductors, a process for forming a superconductor film by using the method, and an apparatus for carrying out the process.
2. Description of the Related Art
The recent research into and development of high temperature superconductors has included an application thereof to electronic elements such as semiconductor devices.
The mechanism of this superconduction is not absolutely clear, however, and a method of evaluating the characteristics of superconductors has not been established. Particularly, in the case of a superconductor film formed by a chemical vapor deposition (CVD), a molecular beam epitaxy (MBE), sputtering, vapor deposition, or the like, the mass to be evaluated is so small that the available evaluation methods are limited in that an evaluation at a required precision is impossible, and this has raised a problem in the developing of a superconductor film having a good crystalline structure and applicable to electronic elements.
Namely, in the conventional evaluation method, the ratio of the number of electrons contributing to a normal conduction to the number of electrons contributing to a superconduction in a superconductor is evaluated by measuring the magnetic susceptibility of the superconductor. The magnetic susceptibility can be measured at a high precision when the mass to be measured has a large volume, such as a bulk material produced by a sintering process or the like, but when the mass to be measured has a minute volume such as a film material, a required sensitivity cannot be obtained and the characteristics of a superconductor cannot be precisely evaluated.
Because the superconductive property of a superconductor depends greatly not only upon the chemical composition thereof but also upon the process conditions during the forming thereof such as the forming temperature, it is necessary to evaluate the characteristics of a superconductor during the growth thereof and to feed back the evaluated results to the process conditions to thereby form a superconductor having a good characteristic. The conventional process and apparatus for forming a superconductor film, however, does not provide a method of evaluating the characteristics of a film during the forming thereof, and thus an effective feedback is not possible.